The present application is based on and claims priority under 35 U.S.C xc2xa7119 with respect to Japanese Patent Application No. 2001-085721 on Mar. 23, 2001 (13th Year of Heisei), the entire content of which is incorporated herein by reference.
1. Field of the Invention
The present invention is generally directed to a fuel-cell cogeneration system of electrical energy and hot water.
2. Description of the Related Art
Each of Japanese Patent Laid-open Print No. Hei-11(1999)-97045 and Japanese Patent Laid-open Print No 2000-67897 discloses a fuel-cell cogeneration system of electrical energy and hot water. In the former, upon high demand for hot water, a reformer is brought into full operation and the resultant surplus hydrogen is stored in a tank. However, the tank is large in scale, thereby enlarging the overall size of the cogeneration system. In addition, the production cost thereof becomes higher.
In the latter, if operation of the fuel-cell stack is initiated while its temperature is low, a wet reformed gas enters the fuel-cell stack, which may close a gas passage in the fuel-cell stack due to a concentration of the water component of the reformed gas, resulting in performance degradation of the fuel-cell stack. To avoid such a problem, the reformed gas should be warmed by a heater before being introduced into the fuel-cell stack, for warming the fuel-cell stack accordingly. Such a structure makes the required time duration to initiate operation of the cogeneration system longer and is followed by energy loss.
Thus, a need exists to provide a fuel-cell cogeneration system of electrical energy and hot water, which is free from the aforementioned drawbacks.
In accordance with a first aspect of the present invention, a fuel-cell cogeneration system of electrical energy and hot water comprises an off gas burner for burning an off gas at an anode of a fuel-cell stack, a reformer including a reformer burner for burning a mixture of air and fuel; a first heat exchanger provided at a downstream-side of stack cooling water, wherein the first heat exchanger is adapted to exchange heat from the off-gas burner with the stack cooling water from the fuel cell, to heat the stack cooling water; and switching means for switching a direction of flow of a reformed gas from the reformer, depending on an operation condition of the system and a demand for the hot water.
In accordance with a second aspect of the present invention, a fuel-cell cogeneration system of electrical energy and hot water is a modification of the first aspect, wherein the switching means is a direction switching valve.
In accordance with a third aspect of the present invention, a fuel-cell cogeneration system of electrical energy and hot water is a modification of the first aspect, wherein the reformed gas is supplied to the off-gas burner for warming the stack cooling water at a warming-up stage of the system.
In accordance with a fourth aspect of the present invention, a fuel cell cogeneration system of electrical energy and hot water is a modification of the first aspect, wherein the reformed gas is supplied to the off-gas burner for warming the stack cooling water upon higher demand of hot water during a steady state operation of the system.
In accordance with a fifth aspect of the present invention, a fuel-cell cogeneration system of electrical energy and hot water is a modification of the first aspect, wherein the reformed gas is supplied to the reformer burner upon higher demand of electricity during a steady state operation of the system.
In accordance with a sixth aspect of the present invention, a fuel-cell cogeneration system of electrical energy and hot water is a modification of the second aspect, wherein the direction switching valve is a first 3-directional switching valve which controls fluid
communication between each of the reformer, the reformer burner and the gas burner.
In accordance with a seventh aspect of the present invention, fuel-cell cogeneration system of electrical energy and hot water is a modification of the sixth aspect, which further comprises a second heat exchanger provided between the reformer and the fuel-cell stack and a second three-way valve which controls a fluid communication between the second heat exchanger and the fuel-cell stack.
In accordance with an eighth aspect of the present invention, fuel-cell cogeneration system of electrical energy and hot water is a modification of the seventh aspect, which further comprises a third heat exchanger provided between the first heat exchanger and the second heat exchanger, the third heat exchanger being adapted to receive the heated stack cooling water and to heat exchange the stack cooling water with a secondary cooling water.
In accordance with a ninth aspect of the present invention, fuel-cell cogeneration system of electrical energy and hot w fuel-cell cogeneration system of electrical energy and hot water, comprises off-gas burner means for burning an off-gas from an anode electrode of a fuel cell; reformer means including a reformer burner for burning a mixture of air and fuel; first heat exchanger means for exchanging heat from the off-gas burner means with the stack cooling water from the fuel cell; and switching means for switching a direction of flow of a reformed gas from the reformer means, depending on an operation condition of the system and a demand for the hot water.